1. Field of the Invention
The present invention relates to a micrometer. More specifically, it relates to a micrometer of which spindle moves at a high speed.
2. Description of the Related Art
Some micrometers move the spindle thereof at a higher speed than the conventional ones.
As shown in FIGS. 1 and 2, such micrometers include a frame 1 having an anvil 2, a spindle 3 advanceable relative to the anvil 2 of the frame 1, an inner sleeve 4 disposed on the frame 1 coaxially with the spindle 3, an outer sleeve 5 rotatably fitted to an outer circumference of the inner sleeve 4, a thimble 7 rotatably provided on an outside of the outer sleeve 5 through a ratchet mechanism 6, a driving means 8 for advancing and retracting the spindle 3 relative to the anvil 2 in accordance with rotation of the thimble 7, a displacement sensor 9 for detecting displacement amount of the spindle 3, and a display 10 for displaying detected value detected by the displacement sensor 9. Reference numeral 12 indicates a power on-off switch.
The driving means 8 includes an engage pin 21 projectingly provided on a rear end of the spindle 3 through a connecting member 20, a slit 22 formed on a circumference of the inner sleeve 4 along an axial direction of the spindle 3 for movably guiding the engage pin 21 in the axial direction of the spindle 3, and a spiral groove 23 formed in spiral on an inner circumference of the outer sleeve 5 around the center of the spindle 3 for engaging the engage pin 21. The pitch of the spiral groove 23 is extremely wider than a conventional screw pitch, which is, for example, approximately ten to twenty times as wide as the screw pitch of the conventional micrometer (ordinarily 0.5 mm pitch).
The displacement sensor 9 has a sensor 26 including a scale 24 formed along a longitudinal direction of the spindle 3 and a detector 25 fixed to the frame 1 spaced apart at a predetermined gap. The displacement sensor 9 converts signal detected by the sensor 26 into a number of pulse signals corresponding to a movement displacement amount of the spindle 3 and counts the pulses.
When the outer sleeve 5 is rotated by rotating the thimble 7, the spindle 3 is advanced and retracted in the axial direction thereof through an engage pin 21 engaging the spiral groove 23 of the outer sleeve 5. At this time, since the pitch of the spiral groove 23 is ten to twenty times as large as the conventional screw pitch, the spindle 3 can be moved approximately ten to twenty times as fast as the conventional one.
Accordingly, even in alternately measuring workpiece having dimension difference, the spindle 3 can be moved at a high speed, thereby efficiently conducting measurement.
According to the above-described high-speed micrometer, since the pitch of the spiral groove 23, i.e. a lead, is large, fluctuation of thrust (thrust force: measurement force) of the spindle 3 according to deviation of driving force (force for rotating the thimble 7) can be restrained. On the other hand, when a user's hand is released from the thimble 7 while the workpiece is sandwiched by the anvil 2 and the spindle 3, the spindle 3 can be backed by the rotation of the outer sleeve 5. This is made possible since a larger rotating force operates on the outer sleeve 5 than the conventional micrometer by virtue of a counterforce provided by the workpiece.
When the spindle 3 is backed, the movement is detected by the displacement sensor 9, which result in a change of displayed value on the display 10.